(1) Field of the Invention
The present invention relates to information processing apparatuses and card-type information processing devices, and more particularly, to an information processing apparatus and a card-type information processing device, each receiving a carrier wave that has been modulated in accordance with information and extracting information and power therefrom to execute a predetermined process.
(2) Description of the Related Art
Recently, a card-type information processing device with a contactless interface has been developed and expected to be placed for not only the personal use such as a credit card or commuter pass but also the industrial use such as a tag in factory automation and product management.
The physical interface prescribed in the ISO/IEC 14443 Part 2 is known as a radio wave interface of such a card-type information processing device. Particularly, a card equipped with a CPU as an LSI for smart cards needs constant supply of power and clock, and therefore employs the Type B specification of the above-mentioned standard.
FIG. 10 is a diagram of a conventional configuration of the card-type device with the contactless interface that matches the Type B specification.
In FIG. 10, a reader/writer 10 is made up of an oscillation circuit 11, an interface (I/F) 12, a modulation circuit 13, a transmitting circuit 14, an antenna 15, a receiving circuit 16, and a demodulation circuit 17. A radio wave is used to send and receive information to and from a card-type information processing device 20.
The oscillation circuit 11 generates a carrier wave of 13.56 MHz.
The I/F 12, which is connected to an upper computer that is not shown for the sake of simplicity, receives information to be sent to the card-type information processing device 20 and outputs information received therefrom.
The modulation circuit 13 modulates the amplitude of the carrier wave from the oscillation circuit 11 (ASK modulation: Amplitude Shift Keying).
The transmitting circuit 14 sends the ASK-modulated carrier wave via the antenna 15.
The antenna 15 radiates the signal supplied from the transmitting circuit 14 in the form of a radio wave, while capturing a radio wave from the card-type information processing device 20 and supplying it to the receiving circuit 16.
The receiving circuit 16 converts the radio wave captured by the antenna 15 into an electric signal.
The demodulation circuit 17 demodulates the electric signal from the receiving circuit 16 to thereby extract information modulated onto the carrier wave.
The card-type information processing device 20 is made up of an antenna 21, a capacitor 22, a full-wave rectifier circuit 23, a capacitor 24, a voltage stabilizing part 25, an ASK demodulator part 26, a capacitor 27, an information processing part 28, a transmitting circuit 29, and a carrier clock extracting circuit 30. The card-type information processing device 20 is driven by power sent by the reader/writer in the form of radio wave. The card-type information processing device 20 retrieves information superimposed in the electric wave, and processes the information in various ways. Resultant information thus obtained is sent back to the reader/writer 10.
The antenna 21 captures the radio wave sent by the reader/writer 10, and radiates the signal from the transmitting circuit 29 toward the reader/writer 10 in the form of radio wave.
The capacitor 22 combines with the inductance component to form parallel resonant circuit, which acts to increase power that can be received by the card-type information processing device 20.
The full-wave rectifier circuit 23 extracts dc power from the received radio wave.
The capacitor 24 eliminates a carrier ripple component overlaid onto the dc power from the full-wave rectifier circuit 23, and generates the ASK modulated wave by envelope detection, as will be described later.
The voltage stabilizing part 25 stabilizes the dc power from which the ripple component has been eliminated at a constant voltage.
The ASK demodulation part 26 extracts information from the signal after the envelope generation through ASK demodulation.
The capacitor 27 eliminates the ripple component contained in the power supply voltage supplied to the information processing part 28.
The information processing part 28 may, for example, be made of a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory) and an encrypt circuit. The information processing part 28 processes information retrieved by the ASK demodulation circuit 26 in various ways.
The transmitting circuit 29 sends the results of information processing by the information processing part 28 to the reader/writer 10 via the antenna 21.
The carrier clock extracting circuit 30 extracts a clock of 13.56 MHz from the received carrier wave of 13.56 MHz, the clock being supplied to the information processing part 28.
FIG. 11 is a diagram of a conventional configuration of the card-type information processing device 20. As shown in FIG. 11, the full-wave rectifier circuit 23 is composed of diodes 23a through 23d. The voltage stabilizing part 25 is composed of a resistor 25a and a voltage stabilizing circuit 25b. The ASK demodulation part 26 is composed of a resistor 26a and an ASK demodulation circuit 26b. 
The diodes 23a through 23d rectify the full wave of an RF signal from the antenna 21 and result in a dc signal.
The resistor 25a makes isolation for eliminating interference between the capacitor 24 and the capacitor 27.
The voltage stabilizing circuit 25b stabilizes the voltage to be supplied to the information processing part 28 at a constant level.
The resistor 26a cooperates with the capacitor 24 and detects the signals from the diodes 23a–23d in envelope detection.
The ASK demodulation circuit 26b ASK-demodulates the detected signal from the resistor 26a and the capacitor 24 to thereby extract information therefrom.
FIG. 12 is a circuit diagram of a conventional configuration of the carrier clock extracting circuit 30. As shown in FIG. 12, the carrier clock extracting circuit 30 includes N-channel MOS-FETs (Metal-Oxide Semiconductor Field Effect Transistor) 30a and 30b, P-channel MOS FETs 30c and 30d, a constant-current source 30e, and a level shift circuit 30f. 
A differential amplifier is formed by the N-channel MOS-FETs 30a and 30b, P-channel MOS-FETs 30c and 30d, and the constant-current source 30e. The differential amplifier amplifies the voltage difference between RF signals RF1 and RF2 from the antenna 21, the amplified difference being applied to the level shift circuit 30f. 
The level shift circuit 30f shifts the level of the signal from the differential amplifier to a level of a digital signal. The output signal of the level shift circuit 30f is a carrier clock.
The conventional device described above operates as follows.
The oscillation circuit 11 generates the carrier wave of 13.56 MHz, which is supplied to the modulation circuit 13. The modulation circuit 13 modulates information to be sent to the card-type information processing device 20 onto the carrier wave from the oscillation circuit 11 in ASK modulation. The modulated carrier wave is sent to the transmitting circuit 14.
The transmitting circuit 14 transmits the radio wave corresponding to the signal from the modulation circuit 13 via the antenna 15.
The antenna 15 radiates the radio wave toward the card-type information processing device 20.
The antenna 21 of the card-type information processing device 20 captures the radio wave emitted by the reader/writer 10, and supplies it to the full-wave rectifier circuit 23. The inductance component of the antenna 21 cooperates with the capacitor 22 to form a parallel resonant circuit, which increase the power that can be received by the card-type information processing device 20.
The diodes 23a–23d rectify the RF signals RF1 and RF2 from the antenna 21.
The capacitor 24 and the resistor 26a eliminate a ripple component overlaid onto the dc signal from the diodes 23a–23d, and detect the envelope of the dc signal by envelope detection.
The ASK demodulation circuit 26b demodulates the envelope-detected signal in ASK to thereby retrieve original information (information item “0” or “1”), which is then supplied to the information processing part 28.
The resistor 25a prevents interference between the capacitor 24 and the capacitor 27. That is, the resistor 25a prevents the ASK signal across the capacitor 24 from being supplied to the information processing part 28.
The voltage stabilizing circuit 25b acts to supply a constant dc voltage to the information processing part 28.
The capacitor 27 eliminates a ripple component contained in the power supply voltage from the voltage stabilizing circuit 25b. 
The differential amplifier, which is made up of the N-channel MOS-FETs 30a and 30b and the P-channel MOS-FETs 30c and 30d amplifies the difference signal between the RF signals RF1 and RF2 with a predetermined gain. This results in a signal of 13.56 MHz. The level shift circuit 30f converts the signal of 13.56 MHz into the level of the digital signal, which is supplied to the information processing part 28 as a clock.
In the above-mentioned manner, the information processing part 28 is supplied with the power from the voltage stabilizing circuit 25b, the received information from the ASK demodulation circuit 26b, and the clock from the carrier clock extracting circuit 30. Then, the information processing part 28 processes the information from the ASK demodulation circuit 26b in a given manner in synchronism with the clock from the carrier clock extracting circuit 30.
The resultant information is sent back to the reader/writer 10 via the transmitting circuit 29.
The reader/writer 10 captures the radio wave returned from the card-type information processing device 20, the radio wave being converted into the electric signal, from which information is extracted by the demodulation circuit 17.
The information thus obtained is transferred to the upper computer via the I/F 12.
Recently, there has been an increasing demand for improvement in the capability of processing of the card-type information processing device 20, and an increased clock frequency has been needed accordingly. However, this increases current consumed in the information processing part 28.
As the power consumption in the information processing part 28 increases, the capacitor 27 is needed to have an increased capacity as large as 1000 pF or more in order to effectively eliminate the ripple component contained in the power supply voltage. In order to establish sufficient isolation from the capacitor 24 for use in reception, the resistor 25a is needed to have a larger resistance value. However, the above necessity may not be permitted in terms of the breakdown voltage. For instance, nowadays, it is not unusual to allow current as large as 10 mA to flow in the information processing part 28. Also, the resistor 25a is often required to have a resistance value equal to or greater than 1 kΩ. When 10 mA current flows through the 1 kΩ resistor, a voltage drop of approximately 10 V occurs. Therefore, the above may not be permitted for circuits consisting of elements with a breakdown voltage approximately equal to 10 V.
If the resistor 25a having a smaller resistance is used, the capacitor 24 for the envelope detection will have an increased capacitance because of the capacitor 27. This deteriorates the envelope detection.
As described above, the card-type information processing device 20 has various unexpected problems occur due to increase in power consumed in the information processing part 28, and no means for solving these problems has not yet been proposed.
Further, in the above-mentioned conventional art, as shown in FIG. 12, the clock is generated in such a manner that the differential signal between RF1 and RF2 is extracted by the differential amplifier, and is level-shifted by the level shift circuit 30f. When the analog signal is converted into the digital signal, the duty ratio may not equal to 50% because of noise and dispersion in performance. This causes unstable circuit operation.